Yes, SssI can be used to generate a positive control for the procedure. We suggest 4 units per μg of DNA for 2 hours. Bisulfate is used to convert unmethylated C to T leaving methylated C as C in the substrate DNA. A sample of modified and unmodified substrate is used in a PCR reaction. The differences seen in sequencing PCR products indicate methylated verses unmethylated regions (1). (1) Frommer, M. et al, Proc. Natl. Acad. Sci. USA (1992) Vol. 89, pp1827-1831.